Lubricating oil composition for gas engines

ABSTRACT

The lubricating oil composition for gas engine of the present invention contains (A) a base oil, (B1) an overbased calcium salicylate, (B2) an overbased sodium sulfonate, (C1) an amine-based antioxidant, and (C2) a phenol-based antioxidant, a total content of the amine-based antioxidant (C1) and the phenol-based antioxidant (C2) being 4 mass % or more on a basis of the whole amount of the composition.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for gas engine, particularly an engine oil to be used for gas heat pumps.

BACKGROUND ART

For air conditioning of buildings and constructions, a gas engine heat pump system and a cogeneration system are put to practical use. In such a system, gas engines utilizing a fuel, such as natural gas, liquefied petroleum gas (LPG), etc., are generally used. In these systems, a maintenance and inspection work is burdensome, and therefore, improvements of the maintenance, such as simplification of inspection, prolongation of maintenance work interval, etc., are an important issue.

Conventionally, in a variety of engine oils, it is general to extend the lifetime by mainly employing a calcium-based detergent or a magnesium-based detergent as a metal detergent and subjecting an antioxidant to optimization or the like, thereby enabling an initial base number to be increased and the base number to be maintained over a long period of time. However, in the metal detergent, it is difficult to increase its quantity due to a restriction of sulfated ash, or the like, and according to the action of the antioxidant alone, it is difficult to increase the base number or drastically improve the base number retention. Furthermore, in gas engines, the combustion temperature is high, and nitrogen oxides are liable to be generated. Thus, the gas engine oil is liable to cause NOx-degradation or high-temperature oxidation degradation, and the base number tends to decrease. For that reason, even if it is contemplated to extend the lifetime of a gas engine oil by a general technique applied to engine oils, it is difficult to make oil change unnecessary over a long period of time.

In addition, as the metal detergent, besides the calcium-based detergent and the magnesium-based detergent, a sodium sulfonate is also known (see, for example, PTLs 1 to 3).

CITATION LIST Patent Literature

PTL 1: JP 6-33083 A

PTL 2: JP 5-194978 A

PTL 3: JP 5-508181 A

SUMMARY OF INVENTION Technical Problem

However, since the sodium sulfonate is low in water resistance, its use for automotive engine oils might be avoided. Actually, the sodium sulfonate is not practically used for gas engine oils.

In addition, conventionally, a replacement cycle of gas engine oils was 4,000 hours to 10,000 hours. In recent years, long-drain properties such that the oil change is unnecessary for a period of time of two times or more of the aforementioned replacement cycle are desired.

In view of the foregoing circumstances, the present invention has been made. A problem of the present invention is to increase an initial base number even without increasing the quantity of a metal and also to suppress the degradation by NOx, thereby maintaining the base number even under contact with NOx over a long period of time at a fixed level or more to extend the lifetime of a gas engine oil.

Solution to Problem

In order to solve the foregoing problem, the present inventor made extensive and intensive investigations. As a result, it has been found that the problem can be solved by not only blending, as a metal detergent, an overbased sodium sulfonate in addition to an overbased calcium salicylate but also blending both a phenol-based antioxidant and an amine-based antioxidant such that a total content thereof becomes large, in a lubricating oil composition for gas engine, leading to accomplishment of the present invention.

Specifically, the present invention provides the following (1) to (10).

(1) A lubricating oil composition for gas engine, containing (A) a base oil, (B1) an overbased calcium salicylate, (B2) an overbased sodium sulfonate, (C1) an amine-based antioxidant, and (C2) a phenol-based antioxidant, a total content of the amine-based antioxidant (C1) and the phenol-based antioxidant (C2) being 4 mass % or more on a basis of the whole amount of the composition. (2) The lubricating oil composition for gas engine as set forth above in (1), further containing (D) a heterocyclic compound selected from a compound represented by the following general formula (I) and a compound represented by the following general formula (II).

In the foregoing formulae, R¹ represents a linear or branched alkyl group having 7 to 17 carbon atoms; and n represents 6 to 18.

(3) The lubricating oil composition for gas engine as set forth above in (1) or (2), further containing (C3) a molybdenum-based antioxidant. (4) The lubricating oil composition for gas engine as set forth above in any of (1) to (3), wherein the total content of the amine-based antioxidant (C1) and the phenol-based antioxidant (C2) is 5 mass % or more on a basis of the whole amount of the composition. (5) The lubricating oil composition for gas engine as set forth above in any of (1) to (4), further containing (B3) a basic calcium sulfonate. (6) The lubricating oil composition for gas engine as set forth above in any of (1) to (5), further containing (E1) a polymethacrylate as (E) a viscosity index improver. (7) The lubricating oil composition for gas engine as set forth above in any of (1) to (6), wherein a calcium content is 0.05 to 0.4 mass %, and a sodium content is 0.005 to 0.1 mass % on a basis of the whole amount of the composition. (8) The lubricating oil composition for gas engine as set forth above in any of (1) to (7), which is used for gas heat pumps. (9) A method for producing a lubricating oil composition for gas engine, including blending (B1) an overbased calcium salicylate, (B2) an overbased sodium sulfonate, (C1) an amine-based antioxidant, and (C2) a phenol-based antioxidant in (A) a base oil to produce a lubricating oil composition for gas engine,

a total blending amount of the amine-based antioxidant (C1) and the phenol-based antioxidant (C2) being 4 mass % or more on a basis of the whole amount of the composition.

(10) A lubricating method for lubricating parts therebetween in a gas engine with the lubricating oil composition for gas engine as set forth above in any of (1) to (8).

Advantageous Effects of Invention

In accordance with the present invention, there is provided a lubricating oil composition for gas engine capable of increasing an initial base number even without increasing the quantity of a metal and also suppressing the degradation by NOx, thereby maintaining the base number even under contact with NOx over a long period of time at a fixed level or more.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are hereunder described in detail.

The lubricating oil composition for gas engine (hereinafter may be referred to simply as “lubricating oil composition”) of the present invention contains (A) a base oil; (B1) an overbased calcium salicylate and (B2) an overbased sodium sulfonate as (B) a metal detergent; and (C1) an amine-based antioxidant and (C2) a phenol-based antioxidant as (C) an antioxidant.

[(A) Base Oil]

The base oil (A) that is used in the present invention is not particularly limited, and an arbitrary mineral oil or synthetic oil conventionally used as a base oil of lubricating oil can be appropriately selected and used.

Examples of the mineral oil include a mineral oil refined by subjecting a lubricating oil distillate that is obtained by distilling under reduced pressure an atmospheric residue given by atmospheric distillation of crude oil, to one or more treatments of solvent deasphalting, solvent extraction, hydro-cracking, solvent dewaxing, catalytic dewaxing, hydrorefining, and the like; a mineral oil produced by isomerizing a wax; and the like. Of those, a mineral oil treated by hydrorefining is preferred. The mineral oil treated by hydrorefining readily improves a % Cp, a sulfur content, and a viscosity index as described later.

Examples of the synthetic oil include polyolefins, such as polybutene, an α-olefin homopolymer or copolymer (e.g., an ethylene-α-olefin copolymer), etc.; various esters, such as a polyol ester, a dibasic acid ester, a phosphate ester, etc.; various ethers, such as a polyphenyl ether, etc.; polyglycols; alkylbenzenes; alkylnaphthalenes; base oils produced by isomerizing GTL WAX; and the like. Of those synthetic oils, polyolefins and polyol esters are especially preferred.

In the present invention, the mineral oils may be used singly or in combination of two or more thereof as the base oil. In addition, the synthetic oils may be used singly or in combination of two or more thereof as the base oil. Furthermore, one or more mineral oils and one or more synthetic oils may be used in combination.

In addition, the lubricating base oil serves as a main component in the lubricating oil composition and is contained in an amount of typically 50 mass % or more, preferably 60 to 97 mass %, and more preferably 65 to 95 mass % relative to the whole amount of the lubricating oil composition.

Although a viscosity of the base oil (A) is not particularly limited, a kinematic viscosity thereof at 100° C. is preferably in the range of from 2 to 15 mm²/s, more preferably in the range of from 2.5 to 12 mm²/s, and still more preferably in the range of from 3 to 6 mm²/s. In the present invention, by regulating the kinematic viscosity of the base oil (A) to a relatively low viscosity as described above, the viscosity of the lubricating oil composition may also be made low, and fuel consumption-saving properties are readily realized. In the present specification, the kinematic viscosity is one measured by the method described in the Examples as described later.

The base oil (A) has a % Cp as measured by ring analysis of preferably 70% or more, and more preferably 80% or more. A sulfur content in the base oil is preferably 300 ppm by mass or less, more preferably 100 ppm by mass or less, and especially preferably 20 ppm by mass or less. The term “% Cp as measured by ring analysis” refers to a proportion (percentage) of paraffin components as calculated by the ring analysis n-d-M method and is measured in conformity with ASTM D-3238. The sulfur content is measured in conformity with JIS K 2541.

In the present invention, as described above, by making the proportion of the paraffin components high and the sulfur content low, the high-temperature oxidation stability of the lubricating oil composition is enhanced, and the oxidation degradation under contact with NOx is readily prevented from occurring.

A viscosity index of the base oil is preferably 100 or more, more preferably 120 or more, and especially preferably 125 or more. When the viscosity index is made high as 100 or more, a change in viscosity of the lubricating base oil with a change in temperature becomes small. In the present specification, the viscosity index is one measured by the method described in the Examples as described later.

[(B) Metal Detergent]

The lubricating oil composition of the present invention contains at least (B1) an overbased calcium salicylate and (B2) an overbased sodium sulfonate as (B) a metal detergent.

Although the overbased calcium salicylate (B1) may make the detergency relatively good, when it is used singly, the base number of a new oil may not be thoroughly enhanced without increasing the quantity of a metal. Furthermore, in the case where the composition is, for example, used under a high-temperature environment upon contact with NOx, the decrease of the base number may not be thoroughly suppressed. In addition, when the overbased calcium salicylate (B1) is used singly, the increase in viscosity is liable to be caused due to NOx-degradation, and it is difficult to realize the desired fuel consumption-saving properties.

Meanwhile, in the present invention, when in addition to the component (B1), the overbased sodium sulfonate (B2) is combined and used, the base number of the new oil can be increased without increasing the quantity of a metal in the lubricating oil composition, and even when used under a high-temperature environment upon contact with NOx, the decrease of the base number can be suppressed. In addition, the increase in viscosity to be caused due to NOx-degradation can be suppressed, and the fuel consumption-saving properties are readily realized.

A total base number (TBN) of the overbased calcium salicylate (B1) is preferably 100 to 400 mgKOH/g. By regulating the TBN to such a range, the formation of a precipitate can be suppressed while making the detergency good. Furthermore, the initial base number is readily relatively increased, and the decrease of the base number to be caused due to NOx-degradation or the like can be appropriately inhibited. From these viewpoints, the TBN of the overbased calcium salicylate (B1) is more preferably 150 to 300 mgKOH/g. The TBN refers to a total base number as measured by perchloric acid method in conformity with JIS K2501.

Specific examples of the overbased calcium salicylate that is the component (B1) include those obtained by overbasing a calcium salt of an alkyl salicylic acid, such as a monoalkyl salicylic acid, a dialkyl salicylic acid, etc. The alkyl group constituting the alkylsalicylic acid is a linear or branched alkyl group having typically about 1 to 100 carbon atoms, preferably about 4 to 30 carbon atoms, and more preferably about 6 to 20 carbon atoms.

A TBN of the overbased sodium sulfonate (B2) is typically higher than the TBN of the overbased calcium salicylate (B1), and it is preferably 300 to 600 mgKOH/g. By regulating the TBN to such a range, the base number of a new oil can be enhanced with a relatively small amount of the component (B2) without forming a precipitate or the like. In addition, the decrease of the base number or the increase in viscosity to be caused due to NOx-degradation or high-temperature oxidation degradation is readily inhibited. From these viewpoints, the TBN of the overbased sodium sulfonate (B2) is more preferably 350 to 550 mgKOH/g.

The lubricating oil composition may further contain (B3) a basic calcium sulfonate as the metal detergent (B). A TBN of the basic calcium sulfonate that is used as the component (B3) is preferably 100 mgKOH/g or less, more preferably 5 to 80 mg/g, and still more preferably 10 to 70 mgKOH/g. By containing the basic calcium sulfonate (B3), the detergency of the lubricating oil composition can be made good.

As the overbased sodium sulfonate (B2), those obtained by overbasing a sodium salt of a sulfonic acid of every kind may be used. As the basic calcium sulfonate (B3), those obtained by basifying a calcium salt of a sulfonic acid of every kind may be used. Examples of the sulfonic acid that is used in each of the overbased sodium sulfonate (B2) and the basic calcium sulfonate (B3) include aromatic petroleum sulfonic acids, alkyl sulfonic acids, aryl sulfonic acids, alkylaryl sulfonic acids, and the like. Specific examples thereof may include dodecylbenzenesulfonic acid, dilaurylcetylbenzenesulfonic acid, paraffin wax-substituted benzenesulfonic acid, polyolefin-substituted benzenesulfonic acid, polyisobutylene-substituted benzenesulfonic acid, naphthalenesulfonic acid, and the like.

The overbased calcium salicylate (B1) is contained in an amount of preferably 0.5 to 8.0 mass %, and more preferably 1.0 to 6.0 mass % on a basis of the whole amount of the composition. When the overbased calcium salicylate (B1) is contained in an amount of 0.5 mass % or more, the function as the detergent is exhibited, and furthermore, when used in combination with the component (B2), the decrease of the base number or the increase in viscosity, which is caused due to the use, is readily suppressed while making the initial base number high. When the amount of the component (B1) is controlled to 8.0 mass % or less, the function corresponding to the addition amount is exhibited.

A content of the overbased sodium sulfonate (B2) may be smaller than the content of the component (B1), and it is preferably 0.05 to 2.0 mass %, and more preferably 0.10 to 0.80 mass % on a basis of the whole amount of the composition. When the component (B2) is contained in an amount of 0.05 mass % or more and used in combination with the component (B1), the initial base number is readily made high, and the decrease of the base number or the increase in viscosity is readily suppressed. When the amount of the component (B2) is controlled to 2.0 mass % or less, the function corresponding to the addition amount can be exhibited.

In addition, in the case where the basic calcium sulfonate (B3) is contained in the lubricating oil composition, its content is preferably 0.5 to 5.0 mass %, and more preferably 0.7 to 2.5 mass % on a basis of the whole amount of the composition. When the component (B3) is contained in an amount of 0.5 mass % or more, the function as the metal detergent can be exhibited, and the detergency of the lubricating oil composition can be made good. When the amount of the component (B3) is controlled to 5.0 mass % or less, the function corresponding to the addition amount can be exhibited.

A calcium content of the lubricating oil composition is preferably 0.05 to 0.4 mass %, more preferably 0.08 to 0.38 mass %, and still more preferably 0.25 to 0.35 mass % on a basis of the whole amount of the composition by incorporating the component (B1) or the components (B1) and (B3) as described above.

A sodium content of the lubricating oil composition is preferably 0.005 to 0.1 mass %, more preferably 0.015 to 0.1 mass %, and still more preferably 0.02 to 0.09 mass % on a basis of the whole amount of the composition, by incorporating the overbased sodium sulfonate as the component (B2). In the light of the above, according to the present invention, the NOx-degradation or high-temperature oxidation degradation can be inhibited while controlling each of the calcium and sodium contents to a relatively low value.

A ratio (Ca/Na ratio) of the calcium content to the sodium content is preferably 2 to 20, more preferably 3 to 15, and still more preferably 5 to 10. When the Ca/Na ratio is allowed to fall within such a range, by using appropriate amounts of the components (B1) and (B2), the decrease of the base number and the increase in viscosity, each of which is caused due to the use, are readily suppressed while making the initial base number good.

[(C) Antioxidant]

The lubricating oil composition of the present invention contains (C1) an amine-based antioxidant and (C2) a phenol-based antioxidant as (C) an antioxidant. In view of the fact that the lubricating oil composition of the present invention contains, in addition to the aforementioned component (B), these two components as the antioxidant, the oxidation stability is increased, and even when used under a high-temperature environment upon contact with NOx, the decrease of the base number or the increase in viscosity can be suppressed, and the extension of lifetime and the saving of fuel consumption can be realized.

In the present invention, a total content of these amine-based antioxidant (C1) and phenol-based antioxidant (C2) is 4 mass % or more relative to the whole amount of the lubricating oil composition. When the aforementioned total content is less than 4 mass %, in the case of being used at a high temperature upon contact with NOx, the oxidation degradation is liable to be caused, whereby the high base number might be hardly maintained and the increase in viscosity might be caused, and therefore, the fuel consumption-saving properties or extension of lifetime would be hardly realized. In order to maintain the high base number over a longer period of time and realize fuel consumption-saving properties and extension of lifetime, the total content of the amine-based antioxidant (C1) and the phenol-based antioxidant (C2) is preferably 5 mass % or more.

The total content of the amine-based antioxidant (C1) and the phenol-based antioxidant (C2) is preferably 10 mass % or less, and more preferably 8 mass % or less relative to the whole amount of the lubricating oil composition in order to exhibit the performance corresponding to the blending amount, although it is not particularly limited to these.

In addition, though a mass ratio (C2/C1) of the phenol-based antioxidant (C2) to the amine-based antioxidant (C1) is not particularly limited, it is preferably about 1/3 to 3/1, and more preferably about 1/2 to 2/1. When the lubricating oil composition contains the both components in amounts to some extent, respectively, the aforementioned performances are readily exhibited.

Examples of the amine-based antioxidant (C1) include monoalkyldiphenylamines having an alkyl group having about 3 to 10 carbon atoms, such as mono-t-butyldiphenylamine, monooctyldiphenylamine, monononyldiphenylamine, etc.; dialkyldiphenylamines, in which each alkyl group has about 3 to 10 carbon atoms, such as 4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine, 4,4′-dihexyldiphenylamine, 4,4′-diheptyldiphenylamine, 4,4′-dioctyldiphenylamine, 4,4′-dinonyldiphenylamine, 4-butyl-4′-octyldiphenylamine, etc.; polyalkyldiphenylamines having 3 or more alkyl groups, in which each alkyl group has about 1 to 10 carbon atoms, such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine, di(2,4-diethylphenyl)amine, di(2-ethyl-4-nonylphenyl)amine, etc.; phenyl-α-naphthylamine types as exemplified by alkyl-substituted phenyl-α-naphthylamines having at least one alkyl group having about 1 to 12 carbon atoms, such as methylphenyl-α-naphthylamine, ethylphenyl-α-naphthylamine, butylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine, nonylphenyl-α-naphthylamine, t-dodecylphenyl-α-naphthylamine, etc.; phenyl-α-naphthylamine; and the like.

Among those, it is preferred that a phenyl-α-naphthylamine type and a dialkyldiphenylamine are used singly or in combination of two or more thereof as the amine-based antioxidant. It is more preferred that both a phenyl-α-naphthylamine type (particularly phenyl-α-naphthylamine) and a dialkyldiphenylamine are used in combination. By using the both in combination in this way, the base number or viscosity of the lubricating oil composition is maintained good over a long period of time, and the lifetime is readily extended. In addition, in the case of using a phenyl-α-naphthylamine type and a dialkyldiphenylamine in combination, it is preferred that the content of the dialkyldiphenylamine is higher than the content of the phenyl-α-naphthylamine type on a mass basis.

Examples of the phenol-based antioxidant (C2) include bisphenol-based antioxidants, such as 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 4,4′-bis(2-methyl-6-t-butylphenol), 2,2′-methylenebis(4-ethyl-6-t-butylphenol), 2,2′-methylenebis(4-methyl-6-t-butylphenol), 4,4′-butylidenebis(3-methyl-6-t-butylphenol), 4,4′-isopropylidenebis(2,6-di-t-butylphenol), 2,2′-methylenebis(4-methyl-6-nonylphenol), 2,2′-isobutylidenebis(4,6-dimethylphenol), 2,2′-methylenebis(4-methyl-6-cyclohexylphenol), 4,4′-thiobis(2-methyl-6-t-butylphenol), 4,4′-thiobis(3-methyl-6-t-butylphenol), 2,2′-thiobis(4-methyl-6-t-butylphenol), bis(3-methyl-4-hydroxy-5-t-butylbenzyl)sulfide, bis(3,5-di-t-butyl-4-hydroxybenzyl)sulfide, thiodiethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], etc.; and monophenol-based antioxidants, such as 2,6-d-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, 2,4-dimethyl-6-t-butylphenol, 2,6-di-t-amyl-p-cresol, n-octyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate, 6-methylheptyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate, etc. Among those, it is preferred to use an ester group-containing phenol.

In addition, the bisphenol-based antioxidant and the monophenol-based antioxidant may be used singly, or the both may be used in combination. From the viewpoint of maintaining the base number or viscosity of the lubricating oil composition good over a long period of time, thereby enabling the lifetime to be extended, it is preferred to use the both in combination. In the case of using both the bisphenol-based antioxidant and the monophenol-based antioxidant, it is better that the content of the monophenol-based antioxidant is higher than the content of the bisphenol-based antioxidant on a mass basis.

It is preferred that the lubricating oil composition of the present invention further contains (C3) a molybdenum-based antioxidant as the antioxidant (C). In the present invention, when in addition to the aforementioned components (C1) and (C2), the molybdenum-based antioxidant (C3) is contained as the antioxidant (C), the degradation by NOx or high-temperature oxidation degradation is more prevented from occurring, whereby the decrease of the base number or the increase in viscosity is more readily inhibited.

As the molybdenum-based antioxidant, molybdenum compounds which have hitherto been known as an antioxidant may be used, and for example, mononuclear molybdenum compounds may be used.

More specifically, there is preferably exemplified a molybdenum/amine complex as the molybdenum-based antioxidant. As this molybdenum/amine complex, a hexavalent molybdenum compound, for example, a compound obtained by allowing molybdenum trioxide and/or molybdic acid to react with an amine compound, for example, a compound obtained by a production method described in JP 2003-252887 A, may also be used. Although the amine compound with which the hexavalent molybdenum compound is allowed to react is not particularly limited, specific examples thereof include a monoamine, a diamine, a polyamine, and an alkanolamine. More specifically, examples of the amine compound may include an alkylamine having an alkyl group having 1 to 30 carbon atoms, such as methylamine, ethylamine, dimethylamine, diethylamine, methylethylamine, methylpropylamine, etc. (these alkyl groups may be either linear or branched); an alkenylamine having an alkenyl group having 2 to 30 carbon atoms, such as ethenylamine, propenylamine, butenylamine, octenylamine, oleylamine, etc. (these alkenyl groups may be either linear or branched); an alkanolamine having an alkanol group having 1 to 30 carbon atoms, such as methanolamine, ethanolamine, methanolethanolamine, methanolpropanolamine, etc. (these alkanol groups may be either linear or branched); an alkylenediamine having an alkylene group having 1 to 30 carbon atoms, such as methylenediamine, ethylenediamine, propylenediamine, butylenediamine, etc.; a polyamine, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, etc.; compounds that are the aforementioned monoamines, diamines or polyamines into which alkyl or alkenyl group(s) having 8 to 20 carbon atoms is further introduced, such as undecyldiethylamine, undecyldiethanolamine, dodecyldipropanolamine, oleyldiethanolamine, oleylpropylenediamine, stearyltertraethylenepentamine, etc., a heterocyclic compound, such as imidazoline etc.; an alkylene oxide adduct of such a compound; a mixture thereof; and the like.

In addition, as the molybdenum-based antioxidant, organic molybdenum compounds including a compound of the following general formula (III) and/or a compound of the following general formula (IV) may also be exemplified. A mixture of the compound of the general formula (III) and the compound of the general formula (IV) is obtained by allowing a fatty oil, diethanolamine, and a molybdenum source to react successively with each other through a condensation method described in, for example, JP 62-108891 A.

In the formulae (III) and (IV), R represents a fatty oil residue, and the fatty oil is a glycerol ester of a higher fatty acid that contains at least 12 carbon atoms and may contain 22 or more carbon atoms. Such an ester is generally known as vegetable and animal oils and fats. Examples of the useful vegetable oils and fats are derived from coconut, corn, cotton seeds, linseed oil, peanuts, soybeans, and sunflower kernels. Similarly, animal oils and fats, such as tallow, etc., may be used.

The molybdenum source may be an oxygen-containing molybdenum compound capable of reacting with an intermediate reaction product of the fatty oil and the diethanolamine to form an ester-type molybdenum complex. In particular, examples of the molybdenum source include ammonium molybdate, molybdenum oxide, and a mixture thereof.

Furthermore, examples of the molybdenum-based antioxidant may include a sulfur-containing molybdenum complex of a succinimide described in JP 3-22438 B and JP 2004-2866 A; and the like.

The lubricating oil composition of the present invention contains the molybdenum-based antioxidant (C3) in an amount of preferably 0.01 to 1 mass %, and more preferably 0.04 to 0.5 mass % relative to the whole amount of the composition. When the molybdenum-based antioxidant is contained in an amount of 0.01 mass % or more, the oxidation degradation or NOx degradation of the lubricating oil composition can be appropriately prevented from occurring. In addition, when the molybdenum-based antioxidant is contained in an amount of 1 mass % or less, the effect corresponding to the addition amount can be exhibited.

When the lubricating oil composition contains the aforementioned molybdenum-based oxidant (C3), the molybdenum content in the composition is preferably 20 to 800 ppm, more preferably 40 to 400 ppm, and still more preferably 50 to 200 ppm on a mass basis.

In addition, the lubricating oil composition may contain, as the antioxidant (C), other antioxidants than the aforementioned components (C1) to (C3), such as a phosphorus-based antioxidant, etc.

[(D) Heterocyclic Compound]

It is preferred that the lubricating oil composition of the present invention further contains (D) a heterocyclic compound selected from a compound represented by the following general formula (I) and a compound represented by the following general formula (II). In the present invention, when the heterocyclic compound (D) is contained, the base number is readily enhanced without increasing the metal content in the composition. In addition, even when the lubricating oil composition is used at a high temperature upon contact with NOx, the enhanced base number is readily maintained, and the increase in viscosity is readily suppressed.

In the general formula (I), R¹ represents a linear or branched alkyl group having 7 to 17 carbon atoms. In the general formula (II), n represents an integer of 6 to 18. The aforementioned alkyl group is one composed of, for example, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17 carbon atoms. n is preferably 6, 8, 10, 12, 14, 16, or 18.

The heterocyclic compound (D) may be produced by a well-known method. Examples of the heterocyclic compound (D) include a 2,2,6,6-tetramethylpiperidino-4-ol ester of an aliphatic carboxylic acid, or esters of lauric acid or stearic acid. As the heterocyclic compound (D), a hindered amine represented by the following formula (I-I) or (II-I) is preferred.

In the lubricating oil composition of the present invention, it is preferred that the heterocyclic compound (D) is contained in an amount of 0.1 to 8 mass % on a basis of the whole amount of the composition. When the content of the heterocyclic compound (D) is 0.1 mass % or more, the base number of the lubricating oil composition is readily improved, and the decrease of the base number or the increase in viscosity is readily inhibited. In addition, when the content of the heterocyclic compound (D) is 8 mass % or less, the effect corresponding to the content can be exhibited. The content of the heterocyclic compound (D) is more preferably 0.3 to 5 mass %, and still more preferably 0.5 to 3 mass %.

[(E) Viscosity Index Improver]

It is preferred that the lubricating oil composition of the present invention further contains (E) a viscosity index improver. Examples of the viscosity index improver (E) include (E1) a polymethacrylate.

As the polymethacrylate (E1), those which have hitherto been known as a viscosity index improver can be used. The polymethacrylate (E1) may be either a dispersion type or a non-dispersion type.

A weight average molecular weight of the polymethacrylate (E1) is typically 10,000 to 1,000,000, preferably 30,000 to 800,000, and more preferably 40,000 to 500,000. When the polymethacrylate is used as the viscosity index improver (E), the viscosity properties are improved, whereby the fuel consumption-saving properties of the lubricating oil composition are readily improved. In addition, in the present invention, in view of the fact that the aforementioned components (B) and (C) are appropriately blended, it becomes possible to prevent a reduction of detergency by the polymethacrylate (E1) from occurring.

The weight average molecular weight is a value measured by GPC using polystyrene as a calibration curve. In detail, the weight average molecular weight is, for example, measured under the following conditions.

Column: Two TSK gel GMH6 columns

Measurement temperature: 40° C.

Sample solution: 0.5 mass % THF solution

Detector: Refractive index detector

Standard: Polystyrene

A content of the viscosity index improver (E) in the lubricating oil composition is preferably 0.1 to 10 mass %, more preferably 0.5 to 8 mass %, and still more preferably 1.0 to 5 mass % relative to the whole amount of the composition.

[Ashless Dispersant]

The lubricating oil composition may further contain an ashless dispersant. Examples of the ashless dispersant include a non-boronated imide-based dispersant, a boronated imide-based dispersant, and a mixture thereof. The non-boronated imide-based dispersant is typically called an imide-based dispersant. As the imide-based dispersant, it is suitable to use a polybutenylsuccinimide. Examples of the polybutenylsuccinimide include compounds represented by the following general formulae (V) and (VI).

In these general formulae (V) and (VI), PIB represents a polybutenyl group, and its number average molecular weight is typically 900 or more and 3,500 or less, and preferably 1,000 or more and 2,000 or less. When the number average molecular weight is 900 or more, there is no concern that the dispersibility is inferior, and when it is 3,500 or less, there is no concern that the storage stability is inferior. In the general formulae (V) and (VI), n is typically an integer of 1 to 5, and more preferably an integer of 2 to 4.

Although a production method of the polybutenylsuccinimide is not particularly limited, the polybutenylsuccinimide can be produced by a known method. For example, the polybutenylsuccinimide can be obtained by allowing a polybutenylsuccinic acid obtained through a reaction between polybutene and maleic anhydride at 100° C. or higher and 200° C. or lower to react with a polyamine, such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, etc.

As the boronated imide-based dispersant, it is preferred to use a boronated polybutenylsuccinimide obtained by allowing a boron compound to act on the non-boronated imide-based dispersant exemplified by the foregoing general formula (V) or (VI).

Examples of the boron compound include a boric acid, a boric acid salt, a boric acid ester, and the like. Examples of the boric acid include orthoboric acid, metaboric acid, paraboric acid, and the like. Suitable examples of the boric acid salt include ammonium salts, such as ammonium borates, for example, ammonium metaborate, ammonium tetraborate, ammonium pentaborate, ammonium octaborate, etc., and the like. Suitable examples of the boric acid ester include esters between a boric acid and an alkyl alcohol (desirably having 1 to 6 carbon atoms), such as monomethyl borate, dimethyl borate, trimethyl borate, monoethyl borate, diethyl borate, triethyl borate, monopropyl borate, dipropyl borate, tripropyl borate, monobutyl borate, dibutyl borate, tributyl borate, etc.

A mass ratio B/N of a boron content B to a nitrogen content N in the boronated polybutenylsuccinimide is typically 0.05 to 3, and preferably 0.2 to 2.

Although a content of each of the boronated succinimide-based dispersant and the non-boronated succinimide-based dispersant (imide-based dispersant) is not particularly limited, it is preferably 0.1 to 15 mass %, and more preferably 0.5 to 8 mass %, respectively relative to the whole amount of the lubricating oil composition. When the content is 0.1 mass % or more, good detergency and dispersibility are obtained, and when it is 15 mass % or less, the effects of detergency and dispersibility corresponding to the content are obtained.

[Anti-Wear Agent]

The lubricating oil composition may further contain an anti-wear agent. Examples of the anti-wear agent include sulfur-containing compounds, such as zinc dithiophosphate, zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides, thiocarbonates, thiocarbamates, etc.; phosphorus-containing compounds, such as phosphite esters, phosphate esters, phosphonate esters, and amine salts or metal salts thereof, etc.; sulfur- and phosphorus-containing compounds, such as thiophosphite esters, thiophosphate esters, thiophosphonate esters, and amine salts or metal salts thereof, etc.; and the like. Of those, zinc dithiophosphate is preferred. More specific examples thereof include zinc dialkyldithiophosphate, and for example, a zinc dialkyldithiophosphate having a primary or secondary alkyl group having 3 to 22 carbon atoms or an alkylaryl group substituted with an alkyl group having 3 to 18 carbon atoms is used.

The anti-wear agent is contained in an amount of typically about 0.1 to 5 mass %, and preferably about 0.3 to 3 mass % on a basis of the whole amount of the composition.

[Pour-Point Depressant]

The lubricating oil composition may contain a pour-point depressant. Examples of the pour-point depressant include an ethylene-vinyl acetate copolymer, a condensate of a chlorinated paraffin and naphthalene, a condensate of a chlorinated paraffin and phenol, a polymethacrylate, a polyalkylstyrene, and the like.

The pour-point depressant is contained in an amount of typically about 0.05 to 3 mass %, and preferably about 0.1 to 1 mass % on a basis of the whole amount of the composition.

[Other Additives]

The lubricating oil composition may further contain, in addition to the aforementioned components, one or more additives, such as a metal deactivator, a demulsifier, an antifoaming agent, etc.

Examples of the metal deactivator include a benzotriazole-based compound, a tolyltriazole-based compound, a thiadiazole-based compound, an imidazole-based compound, a pyrimidine-based compound, and the like.

As the demulsifier, a surfactant is used. Examples thereof include polyalkylene glycol-based nonionic surfactants, such as a polyoxyethylene alkyl ether, a polyoxyethylene alkyl phenyl ether, a polyoxyethylene alkyl naphthyl ether, etc.; and the like.

Examples of the antifoaming agent include a silicone oil, a fluorosilicone oil, a fluoroalkyl ether, and the like.

In order to ensure the fuel consumption-saving properties, it is preferred that the lubricating oil composition of the present invention is low in viscosity. Specifically, the viscosity is preferably less than 16.3 mm²/s, more preferably 5.6 mm²/s or more and less than 12.5 mm²/s, and still more preferably 6.1 mm²/s or more and less than 9.3 mm²/s in terms of a kinematic viscosity at 100° C. In addition, a viscosity index of the lubricating oil composition is preferably 130 or more, more preferably 150 or more, and still more preferably approximately from 170 to 250.

It is preferred that the lubricating oil composition of the present invention is a multi-grade oil capable of being used even at a low temperature while maintaining a lubricating performance at a high temperature. Specifically, it is preferred that a CCS viscosity at −35° C. is 6,200 mPa·s or less, a kinematic viscosity at 100° C. is 6.1 mm²/s or more and less than 9.3 mm²/s, and a high-temperature high-shear viscosity (HTHS viscosity) at 150° C. is 2.6 mPa·s or more. Specific examples of such a lubricating oil composition include those of a 0W-20 grade defined in the Society of Automotive Engineers classification system SAE (J300).

The CCS viscosity means a viscosity as measured in conformity with JIS K2010-1993. The HTHS viscosity at 150° C. is a viscosity as measured using a TBS viscometer (tapered bearing simulator viscometer) by the method of ASTM D4683 under conditions of shear rate: 10⁶ sec-1, rotational rate (motor): 3,000 rpm, rotor/stator clearance: 3 μm, and oil temperature: 150° C.

The lubricating oil composition for gas engine of the present invention is one used as an engine oil that lubricates parts therebetween in a gas engine. The gas engine is one to be used for a gas heat pump, a gas engine cogeneration system, and the like, and it is preferably used for a gas heat pump.

[Production Method of Lubricating Oil Composition]

A production method of lubricating oil composition of the present invention is a method including blending at least the aforementioned components (B1) and (B2) and components (C1) and (C2) in the base oil (A) to obtain a lubricating oil composition. In this production method, one or more components selected from the component (B) other than the components (B1) and (B2), the component (C) other than the components (C1) and (C2), the component (D), the component (E), and other components may be further blended in the base oil (A). The amounts (blending amounts) of these respective components are the same as the aforementioned contents of the respective components, and the properties of the lubricating oil composition and the details of the respective components are the same as those described above, and hence, their descriptions are omitted. In the present production method, the respective components may be blended in the base oil by any method, and a technique thereof is not limited.

The lubricating oil composition that is prepared by blending the components (B1) and (B2) and the components (C1) and (C2), and furthermore, optionally one or more components selected from the component (B) other than the components (B1) and (B2), the component (C) other than the components (C1) and (C2), the component (D), the component (E), and other components is generally one containing these blended materials; however, as the case may be, at least a part of the blended additives may be converted to another compound through a reaction or the like.

EXAMPLES

Next, the present invention is described in more detail with reference to Examples, but it should be construed that the present invention is by no means limited by these Examples.

Various properties were those determined according to the following procedures.

(1) Kinematic Viscosity

The kinematic viscosity is a value as measured using a glass-made capillary viscometer in conformity with JIS K2283-2000.

(2) Viscosity Index

The viscosity index is a value as measured in conformity with JIS K2283.

(3) CCS Viscosity and HTHS Viscosity

The CCS viscosity and HTHS viscosity are each a value as measured according to the method described in the specification.

(4) Base Number

The base number of the lubricating oil composition was measured by a hydrochloric acid method in conformity with JIS K2501-2003.

(5) Calcium, Molybdenum, and Sodium Contents

The calcium, molybdenum, and sodium contents were measured in conformity with JPI-5S-38-03.

(6) Nitrogen Content

The nitrogen content was measured in conformity with JIS K2609-1998.

[Evaluation Method]

The lubricating oil composition of each of the Examples and Comparative Examples was evaluated by the following NOx degradation test.

In a flask used for the test of oxidation stability of internal combustion engine lubricating oils defined in JIS K2514, 6 L/hr of a nitrogen gas containing nitric oxide (NO) in a concentration of 8,000 mass ppm and 6 L/hr of air were blown into 250 mL of a sample oil (lubricating oil composition) in the presence of iron and a copper catalyst (a specimen of an oxidation test of JIS K2514). The base number and the kinematic viscosity at 40° C. were measured, when the oil was subjected to forced degradation for 144 hours and 240 hours while holding the temperature of the sample oil at 140° C. A ratio of the base number after the forced degradation to the base number of a new oil was calculated as a base number retention rate (%) in terms of a percentage. In addition, a ratio of the kinematic viscosity at 40° C. of the oil that was subjected to forced degradation to the kinematic viscosity at 40° C. of the new oil was calculated as a kinematic viscosity ratio.

Examples 1 to 11 and Comparative Examples 1 to 2

Lubrication oil compositions of the Examples and Comparative Examples, were prepared with a formulation shown in Table 1, and properties of each of the lubrication oil compositions were measured. In addition, the lubricating oil composition in each of the Examples and Comparative Examples was evaluated according to the aforementioned evaluation methods.

TABLE 1 Example 1 2 3 4 5 6 7 Blending of lubricating oil composition (A) Base oil mass % 77.07 76.07 77.37 78.07 78.17  77.10 78.07 (B1) Metal detergent mass % 3.24 3.24 3.24 3.24 3.24 3.00 3.24 (B2) Metal detergent mass % 0.24 0.24 0.24 0.24 0.24 0.45 0.24 (B3) Metal detergent mass % 2.00 2.00 2.00 2.00 2.00 2.00 2.00 (C1) Amine-based antioxidant 1 mass % 0.20 0.20 0.20 0.20 0.20 0.20 0.20 (C1) Amine-based antioxidant 2 mass % 2.50 2.50 2.50 2.50 2.50 2.50 2.50 (C2) Phenol-based antioxidant 1 mass % 2.00 2.00 2.00 2.00 2.00 2.00 1.00 (C2) Phenol-based antioxidant 2 mass % 0.50 0.50 0.50 0.50 0.50 0.50 0.50 (C3) Molybdenum-based antioxidant mass % 0.10 0.10 0.10 0.10 0.10 0.10 (D) Hindered amine 1 mass % 1.00 2.00 1.00 1.00 (D) Hindered amine 2 mass % 0.70 (E) Viscosity index improver 1 mass % 2.60 2.60 2.60 2.60 2.60 2.60 2.60 (E) Viscosity index improver 2 mass % (E) Viscosity index improver 3 mass % (E) Viscosity index improver 4 mass % Ashless dispersant 1 mass % 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Ashless dispersant 2 mass % 2.50 2.50 2.50 2.50 2.50 2.50 2.50 Ashless dispersant 3 mass % 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Anti-wear agent mass % 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Pour-point depressant mass % 0.20 0.20 0.20 0.20 0.20 0.20 0.20 Others mass % 0.85 0.85 0.85 0.85 0.85 0.85 0.85 Total mass % 100.00 100.00 100.00 100.00 100.00  100.00 100.00 Properties of composition (new oil) Kinematic viscosity at 40° C. mm²/s 35.17 35.53 35.22 36.25 35.22  35.98 35.73 Kinematic viscosity at 100° C. mm²/s 7.846 8.11 7.859 8.090  7.873 8.037 7.978 Viscosity index — 204 213 204 206 205    206 206 CCS viscosity at −35° C. mPa · s 4900 4850 4850 4950 4800     4950 4950 HTHS viscosity at 150° C. mPa · s 2.62 2.70 2.65 2.64 2.60 2.65 2.63 Base number (hydrochloric acid method) mgKOH/g 11.7 12.7 11.8 11.8 11.5  12.2 11.6 Calcium content mass % 0.30 0.27 0.31 0.31 0.31 0.29 0.31 Molybdenum content ppm 73 66 72 70 2>   71 69 Sodium content mass % 0.04 0.04 0.04 0.04 0.04 0.08 0.04 Nitrogen content mass % 0.27 0.31 0.27 0.23 0.21 0.19 0.21 Evaluation results NOx degradation after 144 hours Base number retention rate (HCL) % 38 40 39 32 28    36 30 Kinematic viscosity ratio (40° C.) — 1.26 1.20 1.20 1.21 1.18 1.19 1.28 NOx degradation after 240 hours Base number retention rate (HCL) % 17 16 14 14 13    18 8 Kinematic viscosity ratio (40° C.) — 1.30 1.28 1.34 1.35 1.39 1.35 1.75 Example Comparative Example 8 9 10 11 1 2 Blending of lubricating oil composition (A) Base oil mass % 77.97 79.34 75.92 78.67 77.92 79.07 (B1) Metal detergent mass % 3.24 3.24 3.24 3.24 3.63 3.24 (B2) Metal detergent mass % 0.24 0.24 0.24 0.24 0.24 (B3) Metal detergent mass % 2.00 2.00 2.00 2.00 2.00 2.00 (C1) Amine-based antioxidant 1 mass % 0.20 0.20 0.20 0.20 0.20 0.20 (C1) Amine-based antioxidant 2 mass % 2.50 2.50 2.50 2.50 2.50 1.50 (C2) Phenol-based antioxidant 1 mass % 1.00 1.00 1.00 1.00 2.00 1.00 (C2) Phenol-based antioxidant 2 mass % 0.50 0.50 0.50 0.50 0.50 0.50 (C3) Molybdenum-based antioxidant mass % 0.20 0.10 0.10 0.10 0.10 0.10 (D) Hindered amine 1 mass % 1.00 1.00 1.00 1.00 1.00 (D) Hindered amine 2 mass % (E) Viscosity index improver 1 mass % 2.60 2.60 2.60 (E) Viscosity index improver 2 mass % 1.33 (E) Viscosity index improver 3 mass % 4.75 (E) Viscosity index improver 4 mass % 2.00 Ashless dispersant 1 mass % 2.00 2.00 2.00 2.00 2.00 2.00 Ashless dispersant 2 mass % 2.50 2.50 2.50 2.50 2.50 2.50 Ashless dispersant 3 mass % 2.00 2.00 2.00 2.00 2.00 2.00 Anti-wear agent mass % 1.00 1.00 1.00 1.00 1.00 1.00 Pour-point depressant mass % 0.20 0.20 0.20 0.20 0.20 0.20 Others mass % 0.85 0.85 0.85 0.85 0.85 0.85 Total mass % 100.00 100.00 100.00 100.00 100.00 100.00 Properties of composition (new oil) Kinematic viscosity at 40° C. mm²/s 35.22 35.49 38.66 32.34 35.22 36.15 Kinematic viscosity at 100° C. mm²/s 7.872 7.779 7.848 8.183 7.859 8.070 Viscosity index — 205 199 180 244 204 206 CCS viscosity at −35° C. mPa · s 4800 4750 4900 5000 5450 5550 HTHS viscosity at 150° C. mPa · s 2.59 2.58 2.64 2.70 2.58 2.64 Base number (hydrochloric acid method) mgKOH/g 12.0 11.8 11.6 11.5 9.92 11.1 Calcium content mass % 0.31 0.31 0.31 0.31 0.34 0.31 Molybdenum content ppm 139 71 69 73 69 68 Sodium content mass % 0.04 0.04 0.04 0.04 0.01> 0.04 Nitrogen content mass % 0.27 0.27 0.27 0.27 0.22 0.17 Evaluation results NOx degradation after 144 hours Base number retention rate (HCL) % 40 39 38 36 23 18 Kinematic viscosity ratio (40° C.) — 1.22 1.19 1.28 1.26 1.25 1.31 NOx degradation after 240 hours Base number retention rate (HCL) % 10 11 10 15 9 4 Kinematic viscosity ratio (40° C.) — 1.29 1.25 1.40 1.38 1.65 1.89

*: The respective components in Table 1 are shown below.

(A) Base Oil:

Group III (API classification), hydrorefined mineral oil, kinematic viscosity at 100° C.: 4.1 mm²/s, viscosity index: 131, n-d-M ring analysis % Cp: 87.6%, sulfur content: 10 mass ppm or less

(B1) Metal Detergent:

Overbased calcium salicylate, TBN (perchloric acid method): 225 mgKOH/g, calcium content: 7.8 mass %

(B2) Metal Detergent:

Overbased sodium sulfonate, TBN (perchloric acid method): 450 mgKOH/g, sodium content: 19.5 mass %

(B3) Metal Detergent:

Basic calcium sulfonate, TBN (perchloric acid method): 17 mgKOH/g, calcium content: 2.35 mass %

(C1) Amine-Based Antioxidant 1:

N-Phenyl-1-naphthylamine

(C1) Amine-Based Antioxidant 2:

Dinonyldiphenylamine (IRGANOX L67, manufactured by BASF SE)

(C2) Phenol-Based Antioxidant 1:

6-Methylheptyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (IRGANOX L135, manufactured by BASF SE)

(C2) Phenol-Based Antioxidant 2:

Thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate](IRGANOX L115, manufactured by BASF SE)

(C3) Molybdenum-Based Antioxidant:

Trade name: MOLYVAN 855 (manufactured by R.T. Vanderbilt Company Inc.), a mixture of [2,2′-(dodecanoylimino)diethanolato]dioxomolybdenum(VI) and [3-(dodecanoyloxy)-1,2-propanediolato]dioxomolybdenum(VI), molybdenum content: 7.9 mass %, nitrogen content: 2.8 mass %

(D) Hindered Amine 1:

Compound represented by the foregoing formula (I-I) (XPDL 590, manufactured by BASF SE)

(D) Hindered Amine 2:

Compound represented by the foregoing formula (II-I) (TINUVIN 770, manufactured by BASF SE)

(E) Viscosity Index Improver 1:

Polymethacrylate, weight average molecular weight: 400,000

(E) Viscosity Index Improver 2:

Polymethacrylate, weight average molecular weight: 420,000

(E) Viscosity Index Improver 3:

Polymethacrylate, weight average molecular weight: 45,000

(E) Viscosity Index Improver 4:

Polymethacrylate, weight average molecular weight: 370,000

Ashless Dispersant 1:

Polybutenylsuccinimide, nitrogen content: 2.1 mass %

Ashless Dispersant 2:

Polybutenylsuccinimide, nitrogen content: 1.15 mass %

Ashless Dispersant 3:

Boron-modified polybutenylsuccinimide, nitrogen content: 1.76 mass %, boron content: 2.0 mass %

Anti-Wear Agent:

Zinc secondary-dialkyldithiophosphate, phosphorus content: 8.2 mass %, zinc content: 9.0 mass %, sulfur content: 17.1 mass %

Pour-Point Depressant:

Acrylic acid copolymer

Others:

Metal deactivator, antifoaming agent, demulsifier, and other components

As is evident from the foregoing Examples, by blending the components (B1), (B2), (C1), and (C2) and regulating the total content of the components (C1) and (C2) to 4 mass % or more, the base number of the new oil could be increased, and even when the composition was brought into contact with NOx at a high temperature over a long period of time, the decrease of the base number or the increase in viscosity could be inhibited. In addition, as is evident from Examples 1 to 6, by regulating the total content of the components (C1) and (C2) to 5 mass % or more, the decrease of the base number or the increase in viscosity could be inhibited over a longer period of time. In addition, it can be understood that by blending the component (C3) or the component (D), the decrease of the base number or the increase in viscosity is readily inhibited.

On the other hand, in Comparative Example 1, since the component (B2) was not blended, even though the amount of the component (B1) was increased, the base number of the new oil was not thoroughly increased, and when brought into contact with NOx at a high temperature, the base number was decreased for a relatively short time, and the satisfactory performance was not obtained. In addition, in Comparative Example 2, in view of deceasing the total content of the components (C1) and (C2), when brought into contact with NOx at a high temperature, the base number was decreased for a relatively short time, and the satisfactory performance was not obtained.

INDUSTRIAL APPLICABILITY

The lubricating oil composition for gas engine of the present invention is able to increase an initial base number even without increasing the quantity of a metal and also to suppress the degradation by NOx, thereby maintaining the base number even under contact with NOx over a long period of time at a fixed level or more, and it is suitably useful for gas engines, such as a gas heat pump, a gas engine cogeneration system, etc. 

1: A lubricating oil composition for gas engine, comprising (A) a base oil, (B1) an overbased calcium salicylate, (B2) an overbased sodium sulfonate, (C1) an amine-based antioxidant, and (C2) a phenol-based antioxidant, a total content of the amine-based antioxidant (C1) and the phenol-based antioxidant (C2) being 4 mass % or more on a basis of the whole amount of the composition. 2: The lubricating oil composition for gas engine according to claim 1, further comprising (D) a heterocyclic compound selected from the group consisting of at least one a compound represented by the following general formula (I) and at least one compound represented by the following general formula (II):

wherein R¹ represents a linear or branched alkyl group having 7 to 17 carbon atoms; and n represents 6 to
 18. 3: The lubricating oil composition for gas engine according to claim 1, further comprising (C3) a molybdenum-based antioxidant. 4: The lubricating oil composition for gas engine according to claim 1, wherein the total content of the amine-based antioxidant (C1) and the phenol-based antioxidant (C2) is 5 mass % or more on a basis of the whole amount of the composition. 5: The lubricating oil composition for gas engine according to claim 1, further comprising (B3) a basic calcium sulfonate. 6: The lubricating oil composition for gas engine according to claim 1, further comprising (E1) a polymethacrylate as (E) a viscosity index improver. 7: The lubricating oil composition for gas engine according to claim 1, wherein a calcium content is 0.05 to 0.4 mass %, and a sodium content is 0.005 to 0.1 mass % on a basis of the whole amount of the composition. 8: The lubricating oil composition for gas engine according to claim 1 that is suitable for use in a gas heat pump. 9: A method for producing a lubricating oil composition for gas engine, comprising blending (B1) an overbased calcium salicylate, (B2) an overbased sodium sulfonate, (C1) an amine-based antioxidant, and (C2) a phenol-based antioxidant in (A) a base oil to produce a lubricating oil composition for gas engine, a total blending amount of the amine-based antioxidant (C1) and the phenol-based antioxidant (C2) being 4 mass % or more on a basis of the whole amount of the composition. 10: A composition comprising a base oil, an overbased calcium salicylate, an overbased sodium sulfonate, an amine-based antioxidant, and a phenol-based antioxidant, a total content of the amine-based antioxidant and the phenol-based antioxidant being 4 mass % or more based on the total mass of the composition. 11: A gas engine comprising the composition of claim
 10. 